1. Field of the Invention
The present invention relates to evaluation apparatuses, evaluation methods, storage media which store programs, and programs, for evaluating color reproducibility.
2. Description of the Related Art
In methods for objectively evaluating the color reproducibility of image processing apparatuses or display/recording apparatuses which perform color matching, colors of an image to be evaluated are first measured with a colorimeter, such as a spectrocolorimeter, which can measure colors with high precision. The measured color values (colorimetric values) obtained from the calorimeter, such as CIEL*a*b*, are then compared with the color values of a reference image or a suitable color-reproducibility image to obtain color differences, CIEΔE*ab, of the measured color values of the evaluated image. Color reproducibility is evaluated by the magnitudes of the color differences.
To accurately evaluate the color reproducibility of an apparatus which executes color matching, it is necessary to use as many evaluation colors as possible. Standard color separation data in four-color offset printing, for example, ISO 12642 (1996) specifies 928 evaluation colors. When so many evaluation colors are used to evaluate color reproducibility, it is necessary to perform comparison for evaluation scales, such as a color difference, separately for each evaluation color and to determine the level. This is a complicated and troublesome process.
A general color-reproducibility evaluation method, disclosed in Japanese Unexamined Patent Application Publication No. Hei-9-218956, uses the color difference ΔE*ab(ave)RMS of CIEL*a*b* for the average color-shift amount for ideal color reproduction. The average color difference ΔE*ab(ave)RMS indicates, however, just one part of the characteristics of color reproducibility for many evaluation colors.
There is, for example, a technology disclosed in “Color Management System Evaluation Reference” written by Alfons Ritzeretal, Cohan Technology R&D Laboratory that uses many evaluation scales. This technology is known as a method for synthetically handling many evaluation colors. This technology statistically expresses color differences ΔE*ab for each of the 928 evaluation colors, described in ISO 12642 (1996), by the average ΔE*ab(ave), standard deviation ΔE*ab(σ), and maximum value ΔE*ab(max). Even when three variates (the average, the standard deviation, and the maximum value) are used to express a multivariate evaluation scale for a plurality of evaluation colors, it is still difficult to intuitively understand the correlation between the three variates and a subjective quality.
Some display/recording apparatuses become unstable when an external factor, such as humidity and temperature, affects the apparatuses. In this case, it is necessary to take a time-sequential evaluation into consideration. There is no report for a case in which data such as time-sequential stability is taken into account.
There is not a case either in which a plurality of evaluation scales for color reproducibility are handled and displayed in a layer manner to collectively handle an overall color-reproduction precision to the color-reproduction precision of each evaluation color.
The above-identified Japanese Unexamined Patent Application Publication, No. Hei-9-218956, discloses an example in which the result of a psychological evaluation and an evaluation scale are associated with, and describes a method for predicting an overall color-image-quality score from the relationship between the result of psychological evaluation and a plurality of evaluation scales. The patent does not describe how to obtain an allowance level. In addition, nothing has been found that describes a method in which a plurality of allowance levels are specified for each user and switched in a desired manner, nor how it is determined that the color-reproduction precision reaches an allowance level.
There is not a report either which describes a function for sorting performance in evaluation colors in an arrangement order, in a descending order (an evaluation color having a higher color-reproduction precision is listed earlier) of precision, and in an ascending order (an evaluation color having a lower color-reproduction precision is listed earlier) of precision and displaying it.
When a color-reproduction precision is determined by evaluation for a plurality of evaluation colors, the above-described technologies does not synthetically handle the color-reproduction precision with the plurality of evaluation colors, and it is difficult to perform a highly precise color-reproducibility evaluation.
Further, a plurality of evaluation scales is not accurately displayed. It is impossible to sufficiently identify a factor which causes a problem in color reproducibility. Therefore, it is difficult to optimize color-image control.
Since an allowance level is set to just one value, when each user has a different allowance level, it is difficult to sufficiently determine the extent to which the color-reproduction precision reaches the allowance level.